To date, indexable inserts have been detachably mounted on cutting tools to machine various types of workpieces. Such indexable inserts, for example, have a general structure such as that shown in FIG. 1. That is, as shown in FIG. 1 which shows the general structure of such a indexable insert, a indexable insert 1 usually has an upper surface, side surfaces, and a lower surface. The lower surface is often mounted on a cutting tool in a detachable manner, and the lower surface which is mounted on a cutting tool in such a detachable manner is referred to as a bearing surface 5. Meanwhile, when the lower surface serves as the bearing surface 5, the upper surface is located on the side that comes into contact with chips during cutting of a workpiece and is referred to as a rake face 2. Each side surface is located on one of the sides that come into contact with a workpiece itself and is referred to as a flank face 3. Parts corresponding to edges where the rake face 2 and the flank faces 3 intersect with each other are referred to as cutting edges 4, which play a key role in cutting. In such a indexable insert 1, a structure is generally used in which the surface of a substrate 10 is covered with a coating layer 11 as shown in FIG. 2. With respect to the coating layer, attempts have been made in which various types of compounds were used and various stresses were imparted (Japanese Unexamined Patent Application Publication No. 06-079502 (Patent Reference 1)).
When such an indexable insert is mounted on a cutting tool, problems may arise in which failures, such as breaking and fracturing, occur in the indexable insert. In many cases, the failures may occur when the indexable insert is fastened with a screw of a cutting tool or a locator.
However, effective means for preventing failures of the indexable insert has not yet been realized. It has been considered that such problems of failures cannot be solved, for example, by changing the type of compound used for the coating layer of the indexable insert and adjusting the stress between the rake face and the flank face (Patent Reference 1).
Patent Reference 1: Japanese Unexamined Patent Application Publication No. 06-079502